Reflecting an electromagnetic wave at a reflector plate in the same direction as the direction of incidence requires that the reflector plate be placed perpendicular to the incidence direction of the electromagnetic wave. Accordingly, when an electromagnetic wave is incident upon the reflector plate from an arbitrary direction, it is not possible to reflect the electromagnetic wave in the same direction as the incidence direction.
Then, it is supposed that combining a plurality of reflector plates will allow an electromagnetic wave incident from an arbitrary direction to be reflected in the same direction as the incidence direction.
However, with this method, the state of polarization of the incident electromagnetic wave cannot be varied. For example, when the incident wave is a linearly polarized wave, the state of polarization is preserved between the incident wave and the reflected wave. In this case, it is not possible to make the direction of polarization of the reflected wave different from the direction of polarization of the incident wave.
Also, when the incident wave is a circularly polarized wave, the reflected wave is a circularly polarized wave whose direction of rotation is opposite to that of the incident wave. In this case, it is not possible to make the direction of rotation of the reflected circularly polarized wave coincide with the direction of rotation of the incident circularly polarized wave.
Accordingly, when an electromagnetic wave is transmitted to a reflector plate, the electromagnetic wave reflected at the reflector plate may not be distinguishable from other electromagnetic waves. It is therefore desired that the state of polarization of the reflected wave can be arbitrarily varied from that of the incident wave.
Also, it is not possible to add information to a received electromagnetic wave by combining conventional reflector plates.